Typically the service pipe is a gas service pipe connected by a tee or bend to a cast iron main. Where the main has been lined with a plastic liner, the service pipe is required to have a plastic pipe installed inside it. An aperture is cut through the wall of the liner at each tee or bend (where the tee or bend joins the main) so that each aperture is aligned with the tee or bend. The cutting of such apertures is achieved, for example, using a machine which travels along inside the plastic liner.